Ocean

An ocean is a large saltwater body, larger than a sea. (A sea is a part of an ocean that is partially enclosed by land.) Earth has one ocean, which covers 71 percent of the planet's surface, according to the National Ocean Service. The world's ocean is geographically divided into five named regions: Atlantic, Pacific, Indian, Arctic, and Southern (or Antarctic). It is the only planet known to have bodies of liquid water on its surface.

Although explorers began plumbing the depths of the oceans around 5000 B.C.E., little was known about the deep ocean. Charting and mapping were limited to areas near shore. Until oceangoing vessels advanced, and explorers could cross the oceans, humankind did not realize how vast the world and its waters were.

The oceans face a number of threats, including pollution and global climate change. Plastic pollution in the Pacific has drawn considerable attention due to reports about the Pacific Garbage Patch. Other threats include environmental disasters, such as oil spills.

Overview

The Pacific Ocean is the world's largest and deepest ocean basin. It covers more than 60 million square miles, accounting for more than 30 percent of Earth's surface, according to the National Ocean Service. It averages a depth of 13,000 feet and contains almost twice the water of the Atlantic Ocean. It got its name from Ferdinand Magellan, who in 1520 described it as pacific, a word that means "peaceful." It is bordered on the east by North and South America and on the west by Asia and Australia.

The Atlantic Ocean, the second-largest basin, is about 41.1 million square miles. It covers about 20 percent of the planet's surface, according to the National Ocean Service. It is named for the Greek god Atlas. It is bordered on the west by North and South America and on the east by Europe and Africa. The Atlantic is divided into two basins, the North Atlantic and the South Atlantic.

The Indian Ocean is the smallest of the three major oceans, accounting for about 20 percent of the world's ocean. It has an area of more than 28.3 square miles and is 12,990 feet at its deepest point. It is located between southern Africa and Australia, although its exact borders are often disputed because of the complex geography of the region.

The Southern Ocean surrounds the continent of Antarctica and is about 7.8 million square miles. Its deepest point is in the South Sandwich Trench, which extends to 23,737 feet. Nations and scientists alike debated the name and size of the ocean, although in 2000 the International Hydrographic Organization voted to call it the Southern Ocean and define its border at 60 degrees latitude. This decision was based in large part on the recognition of the distinct drivers of the Southern Circulation. The Southern Ocean has highly complex ocean currents. The cold air, outgoing radiation, and winds cool the water, which flows northward along the ocean floor. Warmer air from the Atlantic, Indian, and Pacific Oceans flows southward at the surface. The level at which these opposite flows of water meet is rich in phytoplankton and other important food sources for aquatic life.

The Arctic Ocean is the smallest of the five. It is more than 5.42 square miles. The lowest point, Molloy Deep, is about 51,204 feet. Its name comes from the Greek word arktikos, meaning "near the bear" or "northern." The reference is to the constellations Ursa Major and Ursa Minor. The ocean is bordered by six countries: Canada, Denmark (Greenland), Iceland, Norway, Russia, and the United States. The Arctic is characterized by ice pack, which in summer is surrounded by open seas. During the winter, when the sun does not rise above the horizon, the icepack doubles in size.

Modern Challenges

Global climate change and pollution have significantly affected ocean waters. The increased use of fossil fuels, which began during the Industrial Revolution, has added high levels of carbon dioxide to the atmosphere. The ocean absorbs about 30 percent of this carbon dioxide, and as the levels of the gas increase in the atmosphere, they increase in the water as well. According to an article in Mother Jones, ocean acidity at the surface on average is about 30 percent higher than it was two centuries ago, when the Industrial Revolution began.

Chemical reactions occur when seawater absorbs carbon dioxide. This produces hydrogen ions, which causes the water to become more acidic. Some fish are less able to detect predators in acidic waters, making them vulnerable and may affect the food web (the interdependent food chains).

Another effect of the chemical reactions is a decrease in available carbonate ions. Many calcifying organisms including oysters, sea urchins, and corals require carbonate ions to make and maintain their shells. In addition to affecting the food web, this threat to calcifying organisms threatens the livelihoods of fishermen around the world.

Global climate change also contributes to ice melt at the poles. This increases the amount of freshwater that pours into the ocean from rivers and further alters the chemistry of the saltwater body. Changing water temperatures also affect aquatic creatures, many of which have altered their feeding habits as their food has shifted to other areas. It also contributes to the warming of the ocean. In 2023, the average global ocean surface temperature was the warmest it had been in recorded history, and experts expected ocean temperatures to continue to increase.

Oil spills and other disasters can have long-lasting effects on marine life, including marine organisms and waterfowl. For example, an oil spill in the Gulf of Mexico (Atlantic Ocean) in 2010 resulted in the near extinction of the bluefin tuna and dwarf seahorse. This event, the largest accidental spill in history, flooded the ocean with an estimated 210 million gallons of oil.

Plastic pollution has been a concern since the 1990s. Reports of a vortex of trash, including plastics, in the Pacific Ocean led to efforts to reduce the amount of plastic that reaches the ocean. Much of it washes off land, in particular the United States, and tumbles in the waves for about six years before reaching the area between California and Hawaii. For decades, environmentalists have documented cases of sea turtles, birds, and other marine creatures ingesting plastics, often with fatal results.

Researchers examining the plastic pieces in the Pacific discovered a more troubling issue: microplastics, such as those included in toothpastes and soaps as microbeads. Scientists have found that many marine animals, such as fish larvae, ingest microplastics with plankton. Researchers have warned that this puts plastics directly into the food web, including the human food supply. Although some experts have proposed skimming the microplastics out of the water, others have noted that this could also remove vital organisms, including plankton, from the ocean.

Bibliography

"Arctic Ocean." The World Factbook, CIA, 26 Nov. 2024, www.cia.gov/the-world-factbook/oceans/arctic-ocean/. Accessed 6 Dec. 2024.

"Climate Change Indicators: Sea Surface Temperature." US Environmental Protection Agency, June 2024, www.epa.gov/climate-indicators/climate-change-indicators-sea-surface-temperature. Accessed 6 Dec. 2024.

"How Big Is the Atlantic Ocean?" National Ocean Service, 4 Jan. 2021, oceanservice.noaa.gov/facts/atlantic.html. Accessed 6 Dec. 2024.

"How Big Is the Pacific Ocean?" Ocean Explorer/National Oceanic and Atmospheric Administration, oceanexplorer.noaa.gov/facts/pacific-size.html. Accessed 6 Dec. 2024.

"How Many Oceans Are There?" National Ocean Service, 16 June 2024, oceanservice.noaa.gov/facts/howmanyoceans.html. Accessed 6 Dec. 2024.

Knapton, Sarah, and Jonathan Pearlman. "'Great Pacific Garbage Patch' Is a Myth, Warn Experts, as Survey Shows There Is No 'Rubbish Island.'" The Telegraph, 5 Oct. 2016, www.telegraph.co.uk/science/2016/10/05/great-pacific-garbage-patch-is-a-myth-warn-experts-as-survey-sho/. Accessed 6 Dec. 2024.

"Ocean Exploration Timeline." Sea and Sky, 2016, www.seasky.org/ocean-exploration/ocean-timeline-menu.html. Accessed 6 Dec. 2024.

"10 Worst Oil Spills in World History." Cleaner Seas, 27 July 2021, www.cleanerseas.com/10-worst-oil-spills-in-world-history/. Accessed 6 Dec. 2024.

"What Is Ocean Acidification?" National Ocean Service, 16 June, 2024, oceanservice.noaa.gov/facts/acidification.html. Accessed 6 Dec. 2024.

"What is the Great Pacific Garbage Patch?" National Oceanic and Atmospheric Administration, 16 June 2024, oceanservice.noaa.gov/facts/garbagepatch.html. Accessed 6 Dec. 2024.

Whitty, Julia. "10 Key Findings from a Rapidly Acidifying Arctic Ocean." Mother Jones, 7 May 2013, www.motherjones.com/blue-marble/2013/05/arctic-ocean-rapidly-getting-more-acidic. Accessed 6 Dec. 2024.